Harlequins have launched an investigation into how Munster supporters managed to buy thousands of tickets for last Sunday's Heineken Cup quarter-final at the Twickenham Stoop.

In accordance with Heineken Cup rules, Munster were allocated 25% of the available tickets for the match, which equated to 3,750. But in a strongly-worded statement published on the club's website, Quins said it was "obvious from 90 minutes before kick-off" that Munster supporter numbers "exceeded" their ticket allocation.

The club say that no tickets were available for general sale with their allocation going to season ticket holders, officials, the tournament organisers, charities and the players. But despite this, Quins say that tickets were being exchanged on Ebay and through "other unauthorised channels". They also added that "where possible, it tried to identify the source of the tickets, the tickets involved and cancel them".

Quins are now seeking out those who sold their tickets in an attempt to prevent a repeat of Sunday's events. The club added: "Last Sunday, it was obvious from 90 minutes before kick-off that Munster's well organised and wonderful supporters had a presence in the stadium that exceeded the number of tickets officially allocated to them.

"The colourful and vocal support they gave their talented team during the match provided further evidence of this, if it was needed. Given the controlled manner that tickets were made available for the match, it is clear to the club that many of its 'supporters' sold their tickets on to opposition fans.

"To say that this is disappointing for the players, coaches, management and staff of the club is an understatement. The club is determined to identify any person that sold on his or her ticket, and will ensure that last Sunday's outcome is not repeated."